Mark survived because he’s a Viltrumite, so injuries that would kill a human can be survivable for him. In the story, his body can regenerate from extreme trauma, and another Viltrumite, Nolan, also helped stabilize him by putting his organs back in place so he could recover.

Why he lived

  • Viltrumite biology: Their bodies are far tougher and more regenerative than human bodies.
  • Not instantly fatal: Even being disemboweled doesn’t necessarily kill a Viltrumite if the heart and brain are still intact.
  • Recovery period: Mark still needed time to heal after the fight, but he did recover.

Story detail

The most common explanation fans point to is that Mark kept fighting long enough to survive the immediate damage, then his healing kicked in after he was stabilized. Some discussion also notes that the real finishing blow to Conquest came from suffocation, not from the wound itself.

If you want, I can also explain this in the context of the specific Invincible scene.